This invention is directed to the chemical treatment of wood to render the same fire retardant. More particularly, this invention is directed to chemical compositions which impart leach resistant, flame retardancy to wood and which do not make the wood significantly more hygroscopic. More specifically, this invention is directed to the treatment of wood with a chemical composition comprising partially reacted monomethylol dicyandiamide, melamine and phosphoric acid to impart to the wood leach resistant flame retardant properties.
It has become the practice in the wood treating industry to treat wood with chemical compounds to produce flame retardant wood. The chemicals commonly used for this purpose include ammonium phosphate, ammonium chloride, ammonium sulfate, borax, boric acid, phosphoric acid, zinc chloride, and magnesium chloride. These chemicals are impregnated as solutions into the wood where they are deposited within the pores of the wood when the solution evaporates. However, these chemicals are only suitable for treating wood which is not subject to the leaching effect of rain and/or ground water. These chemicals are not suitable for exterior and underground construction where leach resistant fire retardants are necessary. In addition, some of these chemicals are objectionable because they are very corrosive to any metal which may be in cotact with the treated wood. Some of the chemicals also cause an objectionable afterglow with the wood and are detrimental to the structural strength of the treated wood. Moreover, many of these chemicals are hygroscopic which causes the wood to absorb moisture and bloom which makes their use objectionable.
More recently, there has been a trend in the wood treating industry towards fire retardant chemical treatments which have low hygroscopicity and are leach resistant and which can be used for exterior wood. Many of these fire retardant chemical treatments for exterior wood have been based on amine-aldehyde-phosphorus condensation compounds. In accordance with the general practice, wood is impregnated with a solution of an incompletely reacted amine-aldehyde-composition together with an oxy acid of phosphorus. The impregnated wood is then dried and cured.
See for example, Goldstein et al, U.S. Pat. No. 2,917,408 which descloses the preparation of fire retardant wood with a combination of dicyandiamide and phosphoric acid and Goldstein et al, U.S. Pat. No. 3,159,503 which discloses the preparation of fire retardant wood with a combination of dicyandiamide, phosphoric acid and very small amounts of formaldehyde. In addition, see Juneja, U.S. Pat. No. 3,832,316 which discloses a composition for imparting fire retardancy to wood comprising dicyandiamide, melamine, formaldehyde and phosphoric acid and Juneja, Canadian Pat. No. 917,334 which discloses a composition for treating wood to impart fire retardancy thereto comprising dicyandiamide, urea, formaldehyde and phosphoric acid.
It has also been known in the past to treat textile materials with similar compositions. For example, see Pingree et al, U.S. Pat. No. 2,488,034, Juda et al, U.S. Pat. No. 2,628,946, Ford et al, U.S. Pat. No. 2,482,755 and O'Brien et al, U.S. Pat. No. 3,625,753. In particular, see Burrnell et al, U.S. Pat. No. 2,582,961 which discloses compositions for treating textiles to impart fire retardance thereto comprising methylol dicyandiamides, methylol melamines and phosphoric acid.
While most of the above described chemical compositions based on dicyandiamide, melamine, urea, formaldehyde and phosphoric acid are effective for imparting fire retardancy to wood, they suffer from one or more drawbacks. For example, the compositions of Goldstein et al are not leach resistant and are not as effective as desired. Compositions based on the above ingredients are convenient to use when the wood treating is performed at the plant site where the chemical compositions are prepared. For example the dicyandiamide, melamine, formaldehyde and phosphoric acid are prepared as an aqueous solution which is used to impregnate the wood. However, the aqueous solution only has a storage life of several weeks at low temperatures, and, therefore, shipping the final chemical solution to distant treating plants is not practical. The storage life of the treating solution may be extended by not adding the phosphoric acid until the solution is ready to be used. However, solutions of the melamine, dicyandiamide and formaldehyde have limited storage life.
Therefore, it is an object of this invention to provide a leach resistant, fire retardant treatment for wood with low hygroscopicity based on melamine, dicyandiamide, formaldehyde and phosphoric acid. It is also an object of this invention to provide chemical compositions based on dicyandiamide, melamine and formaldehyde which can be shipped economically, have excellent storage life, and which can be dissolved in water and then reacted with phosphoric acid to provide a chemical treating solution which will impart leach resistant fire retardant properties to wood and will not make the wood hygroscopic.